CIFEX Experiment # 6

April 7, 2004.

Flight Scientist for Flight # 8: Eric Wilcox

Flight Scientist for Flight #9: V. Ramanathan

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Flight #8: 6:30 a.m. - 10 a.m.

The front associated with a North Pacific storm passed overnight and we flew to the northwest to sample the clouds behind the front as well as an advancing aerosol plume from the north.  In order to capture developing low clouds we departed early in the morning.  The lowest deck of cloud, extending over 200 miles offshore, was lying entirely below our minimum flight altitude of 1000ft.  A separate layer of broken cloud was found between 3000 and 5000ft extending to about 170 miles offshore.  Between the two cloud layers lay a pristine layer of clear air with particle concentrations less of 150-200/cc.  Cloud drops in the 3000-5000ft cloud layer were predominantly large with many exceeding 18 micron, and drizzle present.  Beyond 200 miles the clouds had diminished considerably and we ascended slowly to 16,000ft to measure the aerosol profile.  CN concentrations were generally 400-500/cc throughout the free troposphere with a peak at 5500ft exceeding 1000/cc.  Clouds between 2000 and 5000ft were sampled after turning back toward Arcata including precipitating clouds with broad drop size distributions extending from 10-50 microns.  At 80 miles from shore, the lowest layer of cloud had risen so that we could sample it at about 1000ft.  Drizzle was observed to the surface with low concentrations of large 20-30 micron drops.

Flight #9: Take off was 11:30 am. Lasted about 3 hrs.

Objective: Sample low clouds under relatively clean conditions and sample the “brown Dust” layer aloft (between 10000 to 15000 ft).

Flew about 250 nm(nautical miles) to 128.15 and 43.5 Lat. An ideal flight for looking at indirect effect. Low clouds extending from about 1000 ft to 4000 ft were observed. Sampled these clouds for about 150 nm(about 1.15 hours each way); then climbed up to 17000 feet; encountered the “brown dust” with 1400 CN at bout 15000 ft; flew along this layer on the return leg. The CN decreased abruptly to about 400 per cc after about 50 nm from the end point. Descended to 4000 ft to start sampling low clouds again for about 100 nm; when close to about 50 nautical miles from the coast climbed back again to about 17000 ft. Did not see the “Brown dust” layer at this location.

The major finding: Very shallow clouds of about 500 to 1000 m thick was drizzling heavily. The drop concentration was about 50 per cc. The mean diameter was close to 20 to 30 nm.

The RADAR was very valuable to locate the cloud tops And bottom in this flight.